Much of refinery processing involves reaction of refinery streams in a hydrogen atmosphere. In order to maximize conversion efficiencies and to maintain catalyst life, excess hydrogen is generally used in the catalytic conversion processes, with the unreacted hydrogen being recovered, purified and repressurized for use as a recycle stream. Such recycle processes are costly, both in energy and in equipment. Some progress has been made in developing methods for using a single hydrogen loop in a two-stage reaction process. U.S. Pat. No. 5,009,768 teaches hydrodemetallizing a high-residual vacuum gas oil and hydroconverting the product from the first reaction zone at deep denitrogenation conditions in a second reaction zone. A cycle oil from an FCC may be added to the feed to the second reaction zone. U.S. Pat. Nos. 4,283,271 and 4,283,272 teach processes for making lubricating oil which include passing a suitable hydrocarbon feed and hydrogen sequentially through a hydrocracking zone, a catalytic dewaxing zone and a hydrotreating zone, all at high pressure and in that order, with purification of the hydrogen gas prior to passage to the dewaxing zone. EP 787787 teaches hydroprocessing in parallel reactors, while hydrogen flows in series between the reactors.
U.S. Pat. No. 3,328,290 to Hengstebeck teaches combining the effluent from a hydrocracking zone with a hydrocarbon feedstock and passing the resultant combined stream through a feed-preparation zone. A heavier liquid effluent, from the liquid effluent from the feed preparation zone, is passed, along with a separated hydrogen-containing gas, to the hydrocracking zone. Hengstebeck does not teach feeding a separate VGO stream to the hydrocracking zone.
Other methods have been proposed for separating partially reacted reactants within a reactor, removing one of the reacting streams (generally either a liquid or a vapor stream) and continuing reaction of the remaining stream. For example, U.S. Pat. No. 3,172,836 teaches a two-stage hydrocracking process, with denitrification being accomplished in the first conversion zone and cracking conversion being accomplished in the second conversion zone. In U.S. Pat. No. 3,172,836, a liquid-vapor separation zone is located between two catalyst beds for withdrawing a normally gaseous fraction and a normally liquid fraction from a first catalyst bed. The normally gaseous fraction, along with a second normally liquid fraction, is then passed downwardly through a second catalyst bed. The normally liquid fraction passed through the second catalyst bed may be a liquid fraction recovered from a distillation of the effluent from the first catalyst bed. In U.S. Pat. No. 4,615,789 a liquid/vapor separator is utilized between catalyst beds to remove liquid from between the beds and permit vapor separated by the separator to pass through catalyst beds below the separator.
U.S. Pat. No. 5,603,824 teaches a reactor having at least a top bed containing a hydrocracking catalyst and a bottom bed containing a dewaxing catalyst. A hydrocarbon feed mixture is separated, with the heavier stream being hydrocracked in the top bed of the reactor and the lighter stream combined with the effluent from the top bed and the combination catalytically dewaxed in the bottom bed.
However, additional developments are needed for hydroconverting dissimilar refinery streams using a single hydrogen source. The present invention is directed to such a process.